Weed and grass trimmers using flexible cutting lines are in widespread use. Many of these trimmers employ a rotatable hub with a short length of nylon or other plastic line extending from the hub. When the hub is rotated, the tip of the line extending from the hub provides the cutting or trimming action. Grass and weed trimmers using this principle of operation have been popular for their versatility of use and because the flexible trim line is safer to use than rigid rotating steel blades.
Various types of trimmer devices have been developed for using such flexible trim lines. Typically, rotating line trimmers or string trimmers employ a line having a generally circular cross section. This line, in many trimmers, is wound on a storage reel in the hub of the device and is played out of a hole in the hub in discrete amounts as the end breaks off or wears off. Other rotatable hub trimmers use fixed lengths of flexible line, which are replaced individually when the line wears down or breaks off.
Generally, the trimmer line which is used in rotating string trimmers is manufactured of extruded nylon monofilament material. The cross-sectional diameters of the line used in the trimmers from a larger cross-sectional diameter for commercial trimmers to smaller diameters in the trimmers sold for intermittent home use. Even though different diameter line sizes are employed, the range of sizes is relatively narrow (typically, 0.050 inches to 0.155 inches in diameter). Trimmer lines which have cross sections other than circular cross sections have been developed in an attempt to provide sharper cutting edges at the point of impact when cutting grass or weeds. Cross-sectional configurations in the form of elongated ribbed lines, or a star-like cross section, or square or triangular cross sections have been developed. The overall cross-sectional dimension, however, still is within the range given above for typical circular lines.
Whether the trim line has a circular cross section or some other cross section, the nylon monofilament line out of which the line is made undergoes relatively rapid wear as a result of the friction or abrasion which takes place when the spinning line contacts the grass and weed stems, as the trimmer is being operated. The rotation of the hub in string trimmers is at relatively high speeds (2,000 to 20,000 RPMs); so that replacement of worn line continuously must be effected during operation of the trimmer. Line wear also has been observed to be greater under dry conditions than under wet or high humidity conditions.
Two United States patents to Proulx U.S. Pat. Nos. 5,807,462 and 5,814,176 are directed to a method for forming double strand monofilament line for use in flexible line trimmers. In the process for forming this line, a final or second tank called a "quench tank" is used to moisten the line prior to reeling it up on a spool. The patents indicate that this is done, since spooled line is inhibited from absorbing moisture in the air; but this is desirable for fresh extruded nylon line from a strength standpoint. When the continuous process of the Proulx patents is examined, it is readily apparent that the line passes through this final quenching tank very rapidly, at best, a matter of a few seconds. This is not sufficient to allow any real moisture absorption into the line during the time it is in the tank. When the line is wound onto a spool, the inner turns may carry and trap moisture droplets on the interior of the spool, since the line is wound rapidly and relatively tightly around the spool. The outer turns of the line are exposed to the air where the moisture droplets may evaporate in a low-humidity ambient air surrounding. As a consequence, the outer line may be relatively dry; whereas the inner line may have excess water trapped between the turns, which results in a leaching of the monomers out of the line. The result is a line of inconsistent quality, having different performance characteristics, depending which part of the spool is taken from for subsequent use. In addition, the line wound on reels, which is common in the manufacture of monofilament line for string trimmers, results in a set or curvature of the line, since the final hardening of the line takes place on the storage reels placed at the end of the assembly line.
It is desirable to provide an improved flexible trim line which overcomes the disadvantages of the prior art, which is preconditioned so as to wear at a reduced rate, and which is packaged to maintain the preconditioning status of the line.